A broad array of electronic systems comprise both a high-speed wired interconnect and a wireless radio receiver. A wired interconnect carrying high-speed data has the undesired effect of radiating part of its electromagnetic (EM) energy, which may result in loss of data fidelity in the wired interconnect on the one hand, and in interference with a radio receive signal on the other hand. The spectrum of electromagnetic interference (EMI) emitted from high-speed wired interconnects may be broad, whereas radio receive signals are typically in a relatively narrow radio frequency range. Unfortunately, high-speed interconnect protocols are generally optimized for data transfer fidelity over the intended wired link and disregard the problem of EMI with wireless radios.
FIG. 1 illustrates an example conventional system 100 with a radio receiver 150 receiving interference radiated from one or more full or partial wired interconnects. With respect to drawings herewith, receivers, whether wired or wireless, may be indicated as Rx, whereas transmitters may be indicated as Tx. The radio receiver 150 generally operates to receive radio signals 142 transmitted by radio transmitter 140, which is generally located outside the system 100. The radio signal 142 may be very weak if the transmitter 140 is at a large distance, or in other words, the capability of radio receiver 150 to receive signals from a faraway transmitter 140 is determined by its capability to receive a weak radio signal 142. EMI that overlaps the spectrum or the frequency range of radio signal 142 generally reduces such capability.
System 100 may include one or more partial or full high-speed wired interconnects. For example, it may partially include wired interconnect 110, comprising a transmitter 110.1 outside of system 100 and a receiver 110.3 inside system 100, electrically coupled by wired link 110.2. Similarly, system 100 may fully include wired interconnect 120, comprising transmitter 120.1, wired link 120.2, and receiver 120.3. Again similarly, system 100 may partially include wired interconnect 130, comprising a transmitter 130.1 inside of system 100 and a receiver 110.3 outside, electrically coupled by wired link 130.2.
Wired interconnect 110 may produce EMI 112, wired interconnect 120 may produce EMI 122, and wired interconnect 130 may produce EMI 132. In general, each and every wired interconnect that carries high-speed data is likely to produce EMI that may effectively lower the capabilities of radio receiver 150 to receive a radio signal 142 from a weak or far away radio transmitter 140.
This problem is very common in many electronic systems, including for example consumer devices such as smartphones, smart TVs, computers, laptops, and tablets. These systems often include multiple radio receivers, as well as multiple partial and full wired interconnects. Some of the current radio systems often affected are WiFi, Bluetooth, GPS, CDMA, LTE, etc. Some popular wired interconnect systems that may cause the problems include serial data systems such as Ethernet, USB, and HDMI; video data buses such as internal and embedded DisplayPort and V-by-One; general memory and data buses for computing such as PCIe, HyperTransport, SAS, and SATA. In some of these cases, data can be bidirectional and each end of the wired interconnect may include both a wired data transmitter and a wired data receiver.
FIG. 2 illustrates a wired interconnect 200 with various locations from which it may radiate energy contained in transmitted data. Transmitter 210 provides a stream of data bits represented as a signal of time-varying voltages and/or currents. This time-varying signal can be translated back to a stream of data bits by receiver 270. To get from transmitter 210 to receiver 270, the signal may be coupled via printed card board (PCB) trace 220 with male/female connector pair 230, cable 240, male/female connector pair 250, and PCB trace 260. The signal could be a single time-varying voltage/current, or it could comprise multiple parallel time-varying voltages/currents. The signal could be single-ended or differential. In respective cases, there could be a single path or multiple parallel paths between transmitter 210 and receiver 270. Due to losses in the EM field, including those that cause EMI, there is potentially a large signal attenuation between transmitter 210 and receiver 270. To provide the receiver 270 with adequate signal, the transmitter 210 may be designed to provide extra energy, worsening EMI. Leak of energy, and hence a cause for EMI, may occur at each of the depicted components 210 through 270. The problem is worst near transmitter 210, PCB trace 220, and connector pair 230, but may persist all the way through receiver 270. Therefore, any part of wired interconnect 200 that may be contained in a system 100 may be cause for EMI concern.
Some wired interconnects do not contain all components depicted in FIG. 2. For instance if the wired interconnect is a memory data bus, block 210 might represent a processor containing both a transmit and receive function, block 270 might represent a memory chip containing both a transmit and receive function, and if the processor 210 and the memory chip 270 are both soldered directly onto a PCB, there may only be PCB traces 220 or 260 in between. Should the memory be part of a memory module, then the memory chip may be soldered onto a different PCB than the processor. In that case, processor 210 would be coupled with connector pair 230 or 250 through PCB traces 220, and memory chip 270 would be coupled with connector pair 230 or 250 through PCB traces 260.
In another example, a notebook computer processor may transmit video data to a display panel. The processor is usually contained in the body of the computer, whereas the display panel is contained in the lid. The processor would hold transmitter 210, which is coupled with a single female connector 230 through PCB wires 220. Cable 240 is a flat cable with wires that are etched from or printed onto a flexible substrate. The cable 240 sticks directly into female connector 230 on one end, and into female connector 250 on the other end. The display panel contains circuitry with receiver 270, which is coupled with connector 250 through PCB traces 260.
Regardless of which components are included in an actual wired interconnect, most or all components may leak energy when high-speed data is passed through, and therefore cause EMI.
Common approaches against EMI include differential signaling and shielded cabling and traces. While useful, the reduction can be limited and still allow significant residual EMI. Placing components far from radio receivers helps too, but can be difficult in systems with small form factors, such as hand-held devices. Radios often use metal shielding and larger antennas and associated cable shielding to protect themselves from EMI. Such solutions may be expensive and only partially effective.
Another problem with uncontrolled radiation of EM energy is that it may be difficult to obtain regulatory approvals, such as from the FCC. Furthermore, there is an unmet need for a method to reduce EMI from a high-speed interconnect without degrading the signal integrity over the interconnect.
Therefore, there is an unmet need for a low-cost method to reduce EM radiation emitted by high-speed wired interconnects.